1. Field of the Invention
The present invention relates to an aromatic polysufone resin composition which exhibits an extremely decreased rate of corrosive gas generation from molded products thereof and which is suitable for electric and electronic parts.
2. Background Information
Aromatic polysulfone resins are materials suitable for electronic parts for which a high dimensional stability and a high heat resistance are required, based on the fact that these resins are amorphous and hence are isotropic and have a small mold shrinkage factor, and have a higher glass transition temperature than other high heat resistance resins, such as polyphenylene sulfides or polyether ketones. Thus, aromatic polysulfone resins maintain their properties, such as mechanical strength, elasticity and creep resistance, at a less lowered level up to a higher temperature as compared with said other resins. Particularly, a material in which an aromatic polysulfone resin is compounded with fibrous materials such as glass fibers exhibits a decreased mold shrinkage factor and improved strength and elasticity and therefore may be applied, for example, to relays, switches, connectors, sockets, coil bobbins and so on.
Since aromatic polysulfone resins have a relatively high melt viscosity, they need a higher molding temperature, injection pressure and molding speed, when they are used for injection molding of electronic parts having a small size and a complicated shape or electronic parts having a thin thickness region. Due to such factors, decomposition gas may be generated by heat during molding and a part of the gas may become occluded in molded products. Said occluded gas may be released from the molded products upon practical use and may create various problems. In particular, when the electronic part is a relay.(or case, base, armature, coil bobbin and the like) and the occluded gas is a corrosive gas, a problem may be created in that metal contacts become corroded to cause insulation failure even if the released amount of occluded gas is very small.
The fact that the gas generated from molded products mainly composed of an aromatic polysulfone resin contains corrosive SO.sub.2 has been confirmed by gas chromatography, mass spectrography and so on. While SO.sub.2 is a gas derived from the aromatic polysulfone resin and it is supposed that the gas is formed by heat decomposition in the course of molding and occluded in the molded products, the details of the mechanism causing its production are still unclear.
On the other hand, as a means for decreasing gas generation, JP-A-60-186561 discloses that generation of corrosive gases such as SO.sub.2 gas and H.sub.2 S gas which may be formed by decomposition of polyphenylene sulfide (PPS) can be decreased by adding a hydrotalcite to the PPS resin. Further, JP-A-62-167356 and JP-A-62-295956 disclose that the formation of corrosive gases can also be decreased by adding zeolites to the PPS resin. In addition, JP-A-2-194056 discloses that generation of corrosive gases and aliphatic hydrocarbons with lower boiling points can be decreased when hydrotalcite or zeolites are added to a resin mainly composed of an aromatic polysulfone resin. Additionally, JP-A-3-199265 discloses that formation of corrosive gases can be reduced by adding magnesium oxide to a polyether sulfone resin. Still, JP-A-3-215560 discloses that formation of corrosive gases can be reduced by adding magnesium carbonate to a polyether sulfone resin.
However, while an effect is obtained in decreasing SO.sub.2 at a specific adding amount when hydrotalcite or zeolites are mixed to an aromatic polysulfone resin in order to decrease the amount of SO.sub.2 gas generated from the aromatic polysulfone resin composition, granulation becomes difficult due to deterioration in winding of the resin mixture around a screw of an extruder for producing a composition or in taking up of strands and thus inconveniences may occur in practical use.
The present invention has the purpose to provide an aromatic polysulfone resin composition which has an extremely decreased rate of corrosive gas generation from molded products thereof, which retains mechanical strength and heat resistance inherent in aromatic polysulfone resin, which is excellent in granulation and molding properties and which is suitable for electric and electronic parts.
As the results of extensive studies conducted to solve the above problems, the present inventors have found that the above purpose can be attained by adding a specific amount of at least one compound selected from oxides, peroxides, double oxides and carbonates of a metal belonging to the Group IA or IIA in the periodic table of elements to an aromatic polysulfone resin.